Fuel injection apparatus

Abstract

A fuel injection apparatus for an engine includes a fuel pump, a common rail, a fuel injection valve, and a pressure detector. The pressure detector detects pressure of fuel as actual fuel pressure. The apparatus compares the actual fuel pressure with target fuel pressure determined based on an operational state of the engine. The apparatus computes at least one of a lift amount, by which a nozzle needle of the valve is displaced from a valve seat of the valve, and a lifting speed, at which the nozzle needle is displaced from the valve seat, to be smaller with an increase of a difference between the target and actual fuel pressures when the actual fuel pressure is greater than the target fuel pressure. The apparatus applies the drive pulse to the drive unit based on the at least one of the lift amount and the lifting speed.

1 . A fuel injection apparatus for an internal combustion engine comprising:
 a fuel pump adapted to discharge fuel;   a common rail adapted to accumulate fuel discharged from the fuel pump;   a fuel injection valve adapted to inject fuel supplied from the common rail into a cylinder of the engine, the fuel injection valve including:
 a nozzle body having an injection orifice and a valve seat; 
 a nozzle needle that is received within the nozzle body, the nozzle needle being engageable with and disengageable from the valve seat such that the nozzle needle closes and opens the injection orifice; and 
 a drive unit adapted to reciprocably displace the nozzle needle in a longitudinal direction of the fuel injection valve in accordance with a drive pulse that is applied to the drive unit; 
   a pressure detector adapted to detect pressure of fuel as actual fuel pressure, which fuel is supplied from the common rail to the fuel injection valve;   comparison means for comparing the actual fuel pressure detected by the pressure detector with target fuel pressure that is determined based on an operational state of the internal combustion engine;   computation means for computing at least one of (a) a lift amount, by which the nozzle needle is displaced from the valve seat, and (b) a lifting speed, at which the nozzle needle is displaced from the valve seat, to be smaller with an increase of a pressure difference between the target fuel pressure and the actual fuel pressure when the comparison means determines that the actual fuel pressure is greater than the target fuel pressure as a comparison result; and   drive means for applying the drive pulse to the drive unit based on the at least one of the lift amount and the lifting speed computed by the computation means.   
   
   
       2 . The fuel injection apparatus according to  claim 1 , wherein:
 the at least one of the lift amount and the lifting speed is the lift amount,   
   
   
       3 . The fuel injection apparatus according to  claim 2 , wherein:
 the computation means computes an injection stop period, during which the fuel injection valve stops injecting fuel, based on the operational state of the engine;   when the injection stop period is shorter than a predetermined time period, the computation means corrects the lift amount of the nozzle needle to become smaller such that an injection rate of the fuel injection valve becomes appropriate for the operational state of the engine.   
   
   
       4 . The fuel injection apparatus according to  claim 3 , wherein:
 the injection rate is an injection quantity of fuel per unit time, which fuel is injected by the fuel injection valve.   
   
   
       5 . The fuel injection apparatus according to  claim 1 , wherein:
 the at least one of the lift amount and the lifting speed is the lifting speed.   
   
   
       6 . The fuel injection apparatus according to  claim 5 , wherein:
 the computation means computes an injection stop period, during which the fuel injection valve stops injecting fuel, based on the operational state of the engine;   when the injection stop period is shorter than a predetermined time period, the computation means corrects the lifting speed of the nozzle needle to become smaller such that an injection rate of the fuel injection valve becomes appropriate for the operational state of the engine.   
   
   
       7 . The fuel injection apparatus according to  claim 6 , wherein:
 the injection rate is an injection quantity of fuel per unit time, which fuel is injected by the fuel injection valve.   
   
   
       8 . The fuel injection apparatus according to  claim 1 , wherein:
 the at least one of the lift amount and the lifting speed includes the lift amount and the lifting speed;   when a target fuel injection quantity is smaller than a predetermined quantity, the computation means computes the lift amount of the nozzle needle to become smaller; and   when the target fuel injection quantity is larger than the predetermined quantity, the computation means computes the lifting speed of the nozzle needle to become relatively smaller.